Electrodeposition Of Ni-Mo-Cu Coatings From High Nickel Matte In Deep Eutectic Solvent

With the development of society and the improvement of people's environmental consciousness,the traditional nickel smelting process has been unable to satisfy the requirements of green and efficient process development.Therefore,seeking for a green,efficient,short-flow industrial technology route to achieve the transition from low value-added raw materials to high value-added materials has become the key to green and efficient processing of nickel resources.This subject combines selective chloride phase reconstitution with deep eutectic solvent electrochemical extraction process to develop an innovative metal extraction process for high nickel matte.The NaCl was used as a solid chlorinating agent to investigate the high nickel matte chlorination roasting process.Reline deep eutectic solvent was used as the leaching agent to extract the valuable metals in the roasting product.Afterwards,Cu-Ni and Ni-Mo-Cu coatings were prepared in the Reline deep eutectic solvent by electrodeposition.The hydrogen evolution performance and hydrogen evolution rate determining step of the coatings were analyzed.The technical feasibility of preparing nickel-based hydrogen evolution material from high nickel matte by short flow was demonstrated.The main research contents are as follows:?1?The priority of sulfides chlorination during the high nickel matte chlorination roasting was analyzed by thermodynamic analysis.The effects of roasting temperature,roasting time and chlorinating agent addition amount on the chlorination roasting process were investigated.The results show that the optimum conditions of the high nickel matte chlorination roasting are chlorination roasting temperature 500?,chlorination roasting time 30 min and chlorinating agent addition amount 40 wt%.The leaching experiments of the high nickel matte roasting product were completed by using Reline deep eutectic solvent as the leaching agent.Under the optimal leaching conditions of leaching?liquid-solid ratio 150 mL/g,leaching time 16 h and leaching temperature 50??,the leaching rates of Ni and Cu were 40.24%and 58.21%.Fe and Co concentrations could be controlled at 14.5 mg/L and 16 mg/L.The leaching slag phases contain NiO,CuO,Na₂Ni?SO₄?₂ and Na₂SO₄.?2?Reline deep eutectic solvent leaches high nickel matte roasting product to obtain Reline leachate,and Reline leachate which contains valuable metals Ni and Cu is used as electrolyte.The electrochemical reduction process of Cu?II?and Ni?II?in Reline deep eutectic solvent was investigated.The electrochemical reduction process of Cu?II?was a two-step reduction process,and the electrochemical reduction process of Ni?II?was an one-step reduction process.The Cu-Ni coating was prepared by electrodeposition process,and the electrodeposition parameters were changed to control the composition,morphology and hydrogen evolution performance of the coating Cu-Ni.The optimum electrodeposition parameters of the Cu-Ni coating are electrolyte temperature 60?,electrodeposition potential-1.0 V and electrodeposition time 30 min.The Tafel slope of the Cu-Ni coating prepared under this electrodeposition condition is 216 mV·dec^-1.The exchange current density of the coating was 2.95×10^-2mA·cm^-2,and the hydrogen evolution overpotential?₁₀ was 297 mV.?3?Hexaammonium molybdate was added to the Reline leachate appropriately,and the Reline deep eutectic solvent containing Ni,Mo,and Cu was used as the electrolyte.The electrochemical reduction process of Mo?VI?in Reline deep eutectic solvent was investigated.Mo?VI?could not be reduced in Reline deep eutectic solvent alone,and Mo?VI?could be only codeposited with Ni?II?.The Ni-Mo-Cu coating was electrodepsited on nickel foam.The three-dimensional framework of the nickel foam improved the electrochemical active area and the hydrogen evolution activity of the material.The optimum electrodeposition parameters of Ni-Mo-Cu coating are electrolyte temperature 70?,electrodeposition potential-1.2 V and electrodeposition time 1 h.The Ni-Mo-Cu coating prepared under this condition was evenly distributed and dense in morphology.The Tafel slope of Ni-Mo-Cu coating is 175 mV·dec^-1.The exchange current density of the coating is 1.30 mA·cm^-2,and the hydrogen evolution overpotential?₁₀ is 93 mV.It can be seen that the Ni-Mo-Cu coating has better hydrogen evolution activity than the Cu-Ni coating.The hydrogen evolution stability of Ni-Mo-Cu coating in alkaline solution was analyzed.After hydrogen production in 1 mol/L KOH solution for 12 hours,the hydrogen activity of the coating was slightly decreased,and the phase did not change.It was found that the coating had good hydrogen evolution stability.The hydrogen evolution rate determining step of Ni-Mo-Cu coating in alkaline solution was explored.The hydrogen evolution process of the coating in alkaline aqueous solution consisted of two steps:charge transfer process and desorption process.The hydrogen evolution rate determining step under low overpotential is charge transfer process.As the hydrogen evolution overpotential increases,the desorption process controls the hydrogen evolution process.